1. Field of the Invention
This invention relates to an ellipsometer that uses light beam having wide cross-section, and more particularly, to the measurement of thin films, such as an oxide film formed on a semiconductor substrate, with high resolution.
2. Description of the Related Art
A known example of the prior art relating to an ellipsometer is U.S. Pat. No. 3,880,524 of Frederic H. Dill et al. issued on Apr. 29, 1975. In this prior art, an analyzer is rotated to change its azimuth and measure the change in the intensity of the transmitted light in order to measure the polarized state of light reflected from a single point on a sample.
However, since only one point on the sample can be measured for a single measurement, an extremely long time is required to measure the entire surface of the sample.
Another constitution is considered in order to speed up this measurement. Namely, light reflected from a sample surface is measured using light having a large cross-section as incident light and a image sensor such as a DDC area sensor. In the case of this constitution, however, since the length of the light path of the reflected light is not constant on the sample surface, it has not been possible to obtain clear images of the sample without being obscured.